Artillery Fungus (Sphaerobolus spp.). Ever hear of it? Well, if you have been getting small black spots on the side of your house, or on buckets left outdoors, etc., then you may very well have this fungus.
About, oh, three or four years ago I started to notice these tiny black dots on the side of my house. They were (are) raised - sort of like my siding was splattered with bits of braille. When I found these dots on some of my plants this year, I decided to send it in to our Cooperative Extension folks for ID. Emily, my "mystery stuff ID person", sent me back a print-out about artillery fungus from the plant clinic at Cornell. If you want to go to it, and see photos, visit http://plantclinic.cornell.edu/FactSheets/artfungus/artilleryfungus.htm.
Here is a quick summary:
The dots are, as I suspected, spores. Or, more specifically, they are spore packets known as peridioles. These packets sit on top of little cup-like cells on the fungi which collect water. When the cups are "full," they turn inside out, popping open the cell and flinging the peridioles up to six meters away! These spore packets have a sticky goo on them that helps them stick to surfaces (like siding and buckets and cars) and makes them essentially impossible to remove. It seems they are very light sensitive, which means they "go to the light." In other words, if your house/car/bucket is light-colored, then they will seek it out.
Where are these fungi growing? And why did they "suddenly" appear a few years ago? Well, it seems they like wood chip mulch (as opposed to bark chip mulch) - exactly the stuff I used to mulch all the garden beds I put in around the back of the house. This also explains why I have these spots on the back of the house, but not on the front or sides (where I have no gardens).
What to do? Sadly, there doesn't seem to be a '"cure." Sometimes the spore packets can be scrubbed off, but you might actually do more damage to the house trying to remove them. Fungicides are not recommended. I guess the only solution is to remove the wood chips and thus the fungus, but this won't help with the spots already on your house/car/bucket. Maybe some clever artist in the family can create a dot-to-dot artwork on the siding...